Mosses, ferns… The secrets of reproduction in non-flowering plants

Why don't some plants flower?

The question of why some plants do not produce flowers lies in the complexity of evolution and the adaptation strategies of plant species. Flower production, although a common method of reproduction, is, in reality, an energetically costly strategy. It requires a substantial investment of resources for growth, the development of colours, fragrances, and nectar production, essential for attracting pollinators.

In the face of these challenges, some plants have opted for alternative, less resource-intensive pathways. These adaptations reflect the ability of plants to evolve and adjust to diverse ecological challenges, thereby increasing resilience and broadening their distribution. By freeing themselves from the need to produce flowers, these plants have been able to colonise habitats where other flowering species could not survive, contributing to the richness and diversity of ecosystems.

In short, to put it simply, flowering plants (or spermaphytes, i.e., trees and leafy shrubs, conifers, vegetable crops, grasses, fruit trees, flowering plants in general…) reproduce mainly by pollination, where pollen from the male flower fertilises the ovule of the female flower, leading to seed formation. This method often depends on pollinators such as insects, birds or wind. By contrast, flowerless plants, such as ferns and mosses, use spores or asexual reproduction to propagate.

Flowering plants produce seeds (here the dandelion), and ferns ensure their reproduction through their spores on the undersides of the fronds

The different types of non-flowering plants

For your information, the so-called ‘vegetal’ kingdom, which previously included terrestrial plants (flowering plants, ferns, mosses and sphagnum) as well as algae and cyanobacteria, is now an obsolete notion. From now on, we will speak of the kingdom Plantae which groups the multicellular, photosynthetic and autotrophic organisms, that is, producing their own organic matter from minerals: the spermatophytes, i.e. flowering plants (from trees to the small annual flowers), the pteridophytes (ferns, but also horsetails and lycophytes) and the bryophytes (mosses, sphagnum and liverworts). Lichens are not classified within the Plantae, as they arise (for the most part) from a symbiosis between a fungus and an alga. Consequently, lichens will be placed in the Fungi kingdom (the fungi), since it is the fungal part that enables reproduction. Until the scientific world decides, once again, to completely overhaul classification…

All that to tell you that when we talk about non-flowering plants, we mean only pteridophytes and bryophytes.

• Ferns and horsetails or pteridophytes are vascular plants characterised by their large fronds and their ability to grow in moist and shady environments. Their reproductive process is fascinating: they use spores rather than seeds. Ferns therefore do not produce flowers, but they have developed a complex vascular system for the transport of water and nutrients, which distinguishes them from mosses and algae ;
• Bryophytes are small non-vascular plants that thrive in damp, cool, and often shaded environments. They absorb water and nutrients directly through their leaves, lacking true roots. Like ferns, mosses reproduce via spores, but they do not have an elaborate vascular system, which limits their size.

Mosses, ferns and horsetails

And what about algae?

Oh dear, it’s complicated! As for algae, it is important to note that they are no longer classified within the Plantae kingdom. Algae constitute a polyphyletic group, meaning that they do not all originate from a single common ancestor. They live primarily in aquatic environments, ranging from freshwater ponds to the vast oceans. And although they share some characteristics with terrestrial plants, such as photosynthesis, algae are distinguished by their morphological diversity and their reproduction, which can be either asexual or sexual. In short, we will leave them aside for this article, as technically they are not plants (at least no longer regarded as such since 1960).

First method: asexual reproduction

As you will have gathered, asexual reproduction in non-flowering plants allows these organisms to multiply without the need for sexual reproduction. In this mode of reproduction, a new individual is created from a single parent plant, which ensures rapid and efficient reproduction, particularly suited to environments where growth conditions are favourable. Moreover, this method of reproduction guarantees that the new plants possess the same genetic characteristics as the parent plant, thereby ensuring a degree of uniformity within the population.

Take the example of mosses that reproduce mainly by fragmentation. This process involves a part of the plant detaching from the main body. This detached part has the capacity to develop into a new independent individual, provided it finds a conducive environment. This method of reproduction ensures rapid colonisation of available spaces, which is crucial for species living in competitive or changing environments.

Mosses spread rapidly across an area by fragmentation

Another example, lycopods or Lycopodium, belonging to the group of ferns and allied plants, have creeping stems that extend over the soil or on other substrates. When these creeping stems come into contact with moist, favourable soil, they can develop new roots and, eventually, new shoots. This process is analogous to layering, well known in the cultivation of flowering plants, where a part of the plant is encouraged to root while remaining attached to the mother plant. Once the new part of the lycopod has established its own roots and begins to grow autonomously, it can become a new plant.

Finally, although horsetails have a life cycle that includes sexual reproduction by spores, they can also reproduce asexually. This occurs via their underground rhizomes. These rhizomes are underground stems that spread horizontally in the soil. From these rhizomes, new shoots can emerge at the surface, giving rise to new plants. This system of rhizomes allows horsetails to rapidly colonise large areas, often forming dense colonies.

Lycopodium and Equisetum arvense

Second method: sexual reproduction without flowers

Even though we’re going to discuss sexual reproduction, it may not strike you as sexy, perhaps even rather off-putting. Consider yourself warned. But recall that asexual reproduction in non-flowering plants leads to low genetic diversity, as the offspring are genetic clones of the parent plant, limiting their ability to adapt to changing environments. By contrast, sexual reproduction, although less common, promotes greater genetic diversity, thereby enhancing the species’ ability to adapt to and survive new environmental challenges.

In ferns

Ferns reproduce sexually via a life cycle that involves two distinct phases: the sporophyte and the gametophyte. The dominant phase is the sporophyte, which is the large green plant we recognise as a fern. This plant produces spores, usually on the undersides of its fronds, in structures called sporangia. When the spores mature and are released, they may germinate to become a gametophyte, also known as a prothallus. The prothallus is a small heart-shaped structure that produces both male gametes (spermatozoa) and female gametes (egg cells). The spermatozoa require water to swim to the egg and fertilise it, resulting in the formation of a new sporophyte, which will then grow to become a new fern.

Spores grouped in sporangia

In horsetails

Horsetails have a life cycle similar to ferns, with sporophyte and gametophyte phases. The sporophyte is the most visible form of the plant, with its characteristic stems. Horsetails produce spores in structures called sporangia, often located at the tips of the stems. Once released, the spores germinate to form gametophytes, which are much smaller and less visible than the sporophytes. These gametophytes will produce male and female gametes. As with ferns, fertilisation requires the presence of water, allowing spermatozoa to swim to the eggs.

Sporphytes on Equisetum arvense

In bryophyta (mosses, Sphagnum…)

Mosses follow a distinct pattern of sexual reproduction. In their life cycle, the gametophyte is the dominant phase, i.e., the green and delicate structure typically associated with mosses. On the gametophytes develop small reproductive structures, the antheridia producing spermatozoa and the archegonia producing eggs. Water also plays a crucial role in moss reproduction, because the spermatozoa require a film of water to reach and fertilise the egg cells in the archegonia. After fertilisation, the zygote develops into a sporophyte, which remains attached to the gametophyte. This sporophyte produces spores which, once released, can germinate to form new gametophytes.

In a damp medium, mosses will proliferate rapidly

Environmental influence and adaptations

Environmental factors such as water and wind play a crucial role in reproduction in non-flowering plants such as ferns and mosses. For ferns, the wind acts as an efficient medium for their lightweight spores, enabling dispersal over long distances. This wind dispersal promotes the colonisation of new habitats and genetic diversification, essential factors for the survival of the species in diverse environments. Similarly, water is a vital element, particularly for the reproduction of mosses, because it not only facilitates the movement of sperm cells toward the eggs during fertilisation, but also contributes to the dispersal of spores in moist conditions.

On the other hand, some non-flowering plants have developed unique adaptations to optimise their reproduction in the face of environmental challenges. Mosses, for example, have the remarkable ability to survive extended periods of desiccation. They can remain dormant in dry conditions, before rapidly resuming growth when humidity returns. This ability to withstand desiccation and to rapidly regenerate is an essential adaptation strategy that allows mosses to thrive in environments where other plants would fail.

Evolution and ecological impact of ferns and mosses

All these plants, having evolved over millions of years, have developed diversified reproduction strategies, such as spore production and asexual reproduction, to ensure their survival in changing environmental conditions. This adaptability has not only ensured their own persistence but has also had a significant impact on biodiversity and nutrient cycles within their ecosystems. By contributing to genetic diversity and actively participating in the life cycles of ecosystems, these plants play a crucial role in maintaining the health and resilience of natural habitats.

Moreover, non-flowering plants have a profound impact on their natural environment. They serve as habitat and a food source for a multitude of organisms, ranging from insects to larger animals, thereby contributing to the complexity of food chains. Their presence is also essential for soil health; as they grow, they help stabilise the soil, prevent erosion and, as they decay, create a substrate for Spermaphyta (flowering plants). This soil-retaining capacity is particularly important in vulnerable areas such as slopes and riverbanks. Thus, by understanding the evolution and ecological importance of these plants, we can better appreciate their indispensable role in the preservation of ecosystems and in promoting biodiversity on our planet.

Mais, non-flowering plants, like ferns and mosses, are also crucial for people, offering medicinal, dietary, and industrial uses, in addition to their aesthetic role in horticulture and landscape design. Their ability to filter pollutants from the air and soil also makes them important players for the environment and human health. Sadly, these plants face growing threats such as habitat loss due to urbanisation, the effects of climate change and pollution.

Found along riverbanks, ferns and mosses help stabilise the banks